Kinetic signatures during a quasi‐continuous lobe reconnection event: Cluster Ion Spectrometer (CIS) observations

Abstract

On 3 December 2001 the Cluster spacecraft observed a long‐lasting lobe reconnection event in the southern high‐latitude dusk magnetopause (MP) tailward of the cusp, during a 4 hour interval of mainly northward interplanetary magnetic field (IMF) and of sub‐Alfvénic magnetosheath flow. Almost all the MP encounters have accelerated flows (for which the Walén test has been successfully verified by Retinò et al. (2005)) as well as a large number of secondary populations related to reconnection, that is, ions of magnetosheath or magnetospheric origin which cross the MP either way. The detailed analysis of the distribution functions shows that the reconnection site frequently moves relative to the spacecraft, but simultaneous measurements by two spacecraft on opposite sides of the reconnection site indicate that the spacecraft's distance from the X line is small, i.e., below 3200 km. The vicinity to the X line throughout the event is probably the reason why the distribution functions characteristics agree with theoretical expectations on both sides of the reconnection site throughout this long event. Moreover, the detailed analysis of the distribution functions shows evidence, during a few time intervals, of dual reconnection, i.e., of reconnection simultaneously going on also in the northern hemisphere.